The present invention relates generally to industrial control and, more particularly, to a drive unit for controlling reciprocating electromagnets.
Vibration welding is an industrial process for creating a weld joint coupling two items, typically formed of thermoplastic material. In a linear vibration welding process, one of two parts is moved to slide across the other in a reciprocating fashion under pressure, creating heat through surface friction that melts and welds the parts together at the interface of the parts. As the melted material cools, a molecular bond is formed between the joined surfaces completing the weld.
Linear vibration welders are designed with electromagnetic heads to reduce wear and the need for lubrication associated with bearing surfaces. To control the motion of the reciprocated part, two electromagnets operate in a reciprocating fashion to move a vibration platen to which the part to be moved is secured. By controlling the amplitude and frequency of the drive signals applied to the electromagnets, the platen can be horizontally reciprocated to facilitate the welding process.
If the drive signals applied to the electromagnets are not precisely controlled, one electromagnet may still be energized as the other electromagnet is activated. Hence, the electromagnets pull the platen in opposite directions. This fighting between the electromagnets, repeated every cycle, increases mechanical stresses on the welder, and reduces the efficiency of the process. Vibration welding operations are controlled based on the amplitude and frequency of the platen movement. Competition between the electromagnets reduces the effectiveness at which these variable may be controlled.
Previous techniques for generating the electromagnet drive signals have involved the use of a 3 phase motor drive unit in conjunction with a Scott-T transformer and filter to perform a 3-2 phase transformation. This approach creates a resonance condition, and the drive signals are not completely synchronized, such that competition exists between the electromagnets.
Hence, it would be desirable to control the electromagnets such that only one of the magnets is activated at any particular time to reduce mechanical stress and increase efficiency.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.